1. Field of the Invention
This invention relates to a ferroelectric material, more particularly to a ferroelectric material including a superlattice structure with remanent polarization exhibiting a linearly positive dependency on a driving voltage.
2. Description of the Related Art
A ferroelectric material is characterized by its ferroelectric characteristic at a temperature lower than a critical temperature (Curie temperature). In the ferroelectric phase, each domain included in the ferroelectric material will exhibit electric-dipole alignment and produce self-spontaneous polarization.
The ferroelectric characteristic of the ferroelectric material can be described by polarization-electric field hysteresis loops. The hysteresis loops gradually saturate with an increase in the applied driving voltage (or electrical field). The remanent polarization of the ferroelectric material will exhibit a non-linear dependency on the applied driving voltage (or electric field). In addition, if the applied electric field is reversed, the remanent polarization will be offset and then be reversed. When the remanent polarization reaches zero during the reversing process, the applied reversed electric field is called a coercive field.
Conventional ferroelectric devices, such as ferroelectric random access memory (FeRAM) or optical devices, are made from the above-mentioned ferroelectric material, such as lead zirconate titanate. The remanent polarization of the ferroelectric material exhibits a non-linear dependency on the applied electric field. Therefore, control of the remanent polarization through adjustment of the applied electric field is difficult.
Therefore, there is still a need in the art to provide a ferroelectric device that has a controllable or predictable remanent polarization.